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In his 11th season, however, Cartwright is fully prepared to add nothing to those career totals.

Cartwright is listed as a running back on the 49ers‘ roster, but his sole duties this season could involve all the dirty work on special teams. Cartwright assumed those responsibilities the past two seasons with the Raiders before signing with San Francisco in March.

After boasting perhaps the NFL’s best special teams last year, the 49ers lost one of their best players from those units when Blake Costanzo signed with the Bears in the offseason. According to the team’s statistics, Costanzo ranked second in special-teams tackles (17) and first in “knock downs” with 27 (no other 49er had more than 11 in that category).

Enter Cartwright, a fire hydrant-size 5-feet-8 and 215 pounds, who combined to collect 23 special-teams tackles the past two seasons in Oakland, ranking second on the team each year.

At 32, he’s survived years of special-teams violence with a commitment to training. A favorite offseason activity: Dannyball.

It’s like volleyball, but painful.

Cartwright hurls a 19-pound medicine ball over the net to an opponent. The games go to 11.

It’s a fittingly arduous training method for a veteran who agonizes each summer. Cartwright could be battling running back Anthony Dixon, a key member of the special teams in 2011, for a spot on the 53-man roster.

“I’m just trying to make this roster and do what they ask me to do,” Cartwright said. “I’m never confident. I’m always fighting. I’m never taking anything for granted. And that’s always been my mind-set going into training camp.”

Back to work: The 49ers will practice from 9:15 a.m. to 12:15 p.m. Monday after taking Sunday off. They will have a mock-game practice Thursday before hosting the Vikings in their preseason opener at 6 p.m. Friday.